The present invention relates to a shoe gap adjusting device for a drum brake, which is manually operated.
A conventional shoe gap adjusting device which is relevant to the present invention is known and disclosed, for example, in Japanese Patent Examined Publication No. 5-65,734.
This patent document discloses a conventional shoe gap adjusting device as illustrated in FIGS. 6 and 7, which is comprised of a stationary cylinder body 51 and a brake actuating piston 52 as shown in FIG. 6.
The brake actuating piston 52 is slidably fitted in the cylinder body 51, and adapted to be extended and retracted by feeding and discharging a brake fluid pressure into and from a pressure chamber 53. The piston 52 presses a brake shoe through the intermediary of a shoe engaging member 54, leftward as seen in FIG. 6, so as to effect a braking action upon extension by the feed of the brake fluid pressure. Meanwhile, the piston 52 is retracted by the force of a return spring which acts upon the brake shoe 55 so as to return the brake shoe 55 to its original position, in order to release the braking upon discharge of the brake fluid.
By the way, an opening is formed in the cylinder body 51, and one end part of the piston 52 is projected through the opening. This opening is covered with an elastic boot 56 for dust-proof and water-proof measures. Further, a shoe gap adjusting ring 57 is arranged adjacent to the opening in the cylinder body 51.
The shoe gap adjusting ring 57 also serves as a protecting member for protecting the elastic boot 56 from being damaged, and is arranged adjacent to the elastic boot 56 for covering the latter while it is fitted in the projecting end part of the piston 52 and prevented from rotation. Further, the ring 57 is formed therein with a cut-out groove 57a which serves to receive a tool for rotating the same.
The shoe engaging member 54 is fitted with the front end face of the projecting end part of the piston in a form-locking manner so as to be relatively rotatable as shown at 54a. The shoe engaging member 54 is elastically attached to the projecting end part of the piston 52 through the intermediary of a clip 58 fitted to the projecting end part of the piston 52, in order to prevent the shoe engaging member 54 from coming off and being lost.
The clip 58 grips the shoe engaging member 54 as particularly shown in FIG. 7, and has an annular shape. Specifically, the clip 58 is comprised of an annular elastic support piece 58a for gripping the shoe engaging member 54, an annular elastic piece 58b adapted to be elastically fitted on the projecting end part of the piston 52 so as to prevent the shoe gap adjusting ring 57 from coming off, as well as a connecting part 58c bridging between these pieces 58a, 58b.
Upon adjustment of the shoe gap, which is required for replacement of the brake shoes or the like, a minus screw driver or the like tool is inserted from outside of a drum brake. After the tip end of the tool has been engaged in the cut-out groove 57a of the shoe gap adjusting ring 57, the shoe gap adjusting ring 57 is rotated by the tool.
At this stage, the piston 52 is pressed by the elastic force of the shoe return spring, through the intermediary of the shoe engaging member 54, toward right as seen in FIG. 6. The conical tip end face 59a of the adjusting bolt 59 threaded into the piston 52 inhibits rotation of the adjusting bolt 59 through the frictional contact with the cylinder body 51.
Thus, the rotation of the shoe gap adjusting ring 57 causes the rotation of the piston 52 only, and the shoe gap can be adjusted by the action of the threaded part 59b therebetween, in association with the rotation of the piston 52 relative to the adjusting bolt 59.
By the way, the larger the cut-out groove 57a, the easier the work in which the tip end of the tool is engaged in the cut-out groove 57a of the shoe ring adjusting ring 57. In the above-mentioned conventional shoe gap adjusting device, however, since the shoe gap adjusting ring 57 also serves as a protecting member for the elastic boot 56, if the cut-out groove 57a formed therein is excessively large, the elastic boot 56 is apt to be damaged by the tool thereby giving rise to a tendency that the protecting function for the elastic boot 56 becomes insufficient.
On the contrary, should the size of the cut-out groove 57a be small in order to sufficiently protect the elastic boot 56, the engagement of the tip end part of the tool into the cut-out groove 57a becomes more difficult, and this results in such a problem that the shoe gap adjustment becomes more difficult.
For overcoming the above-mentioned problems, it may be considered that an additional protecting member for protecting the elastic boot 56 is interposed between the elastic boot 56 and the shoe gap adjusting ring 57, in order to allow the shoe gap adjusting ring 57 to eliminate the necessity of the provision of the protecting function for the elastic boot 56.
However, it has been confirmed that the above-mentioned measure is not practical since an additional component is required as the protecting member for the elastic boot, giving rise to disadvantage in terms of added cost in combination with increased number of components.
Further, in the above-mentioned conventional device, the clip 58 for elastically fitting the shoe engaging member 54 in the piston 52 is substantially complicated in shape so that the disadvantage in terms of cost has been unavoidable.